Vertical round container for storing liquids, and arrangement comprising a plurality of containers

ABSTRACT

A vertical round container ( 1 ) for storing liquids comprises a floating cover ( 6 ) covering the surface of the liquid. The cover is sealed in relation to the container wall by means of flexible sealing elements ( 18, 19 ) and includes, on the lower side thereof, at least one compartment ( 62 ) which is open towards the liquid and contains gaseous media/vapors. Devices ( 40   a ) are provided for determining the submersion depth of the cover, and supply/discharge lines ( 29 ) are provided for modifying the quantity of the gaseous medium in the at least one compartment. The supply/discharge lines for the gaseous medium are connected to a central unit ( 28 ) provided outside the container region.

The present invention relates to a vertical round container for storing liquids, comprising a floating cover covering the surface of the liquid, the cover being sealed in relation to the container wall by means of flexible sealing elements and comprising, on the lower side thereof, at least one compartment which is open towards the liquid and in which gaseous media/vapors are entrapped, devices being provided for determining the immersion depth of the cover, and supply/discharge lines being provided for varying the amount of the gaseous medium in the at least one compartment.

Such a cover is known from EP 0 059 298 A1.

Floating covers of liquid surfaces have the function to suppress the exchange between the two fluid media, liquid and gaseous environment.

An important application is presented by large-volume storage containers for highly volatile mineral oil products. To solve the main problem, viz. to prevent fire and explosion, and to avoid emissions, the floating cover was developed 80 years ago.

Following this development two main principles were pursued, namely a tank or container with floating cover without fixed roof (also called external floating roof tank) and a tank with fixed roof and inwardly located floating cover (also called internal floating roof tank).

Since the problems created by residual emissions and precipitations in a container without fixed roof have not been solved in a satisfactory way, preference has recently most of the time been given to a container with fixed roof. The possibility has here been seen to dissolve emissions almost completely with the help of vapor swinging with corresponding containers and vapor recovery and to dispense with the floating cover in the end.

The resulting technique, however, has decisive drawbacks.

All of the completely closed containers containing hydrocarbon vapors present a high risk of explosion and fire and are sensitive to vacuum and overpressure. The daily tank breathing by expanding and contracting gases in the container headspaces requires additional gas containers and the treatment of large gas volumes.

Vapor recovery is expensive and energy-consuming, and the total emission balance becomes negative as compared to containers with a floating cover.

It has therefore been evident that the most expedient methods for minimizing facility risks, total emissions and financial expenditure in storing highly volatile and combustible liquids is the floating cover and that this technique cannot be abandoned. Ideally, the exchange balance between liquid and vapor must be established underneath the floating cover in closed chambers, so that evaporation comes to a standstill. However, this ideal case cannot be maintained permanently due to the necessary operating processes in the container and the presently used constructional solutions.

In practice, welded constructions of steel are exclusively used for external floating covers for refinery products. There are various other constructions for internal floating covers in the form of aluminum member structures with vapor chamber between membrane and liquid level and plastic membranes with direct contact with the liquid.

The above-mentioned EP 0 059298 A1 describes a floating cover for liquid containers which consists of a steel membrane slightly inclined towards the center, a wall on the peripheral side that extends from the plane of the membrane both upwards and downwards, with vapor cushions formed between membrane and liquid level underneath the membrane through a plurality of vertical partitions, the cushions carrying the floating roof. The immersion depth of the floating roof is measured, and the floating position of the roof can be trimmed by adding compressed air into individual buoyancy compartments. Excessive vapor or gas amounts underneath the roof are discharged into the atmosphere. There is no pronounced water collection zone in this floating roof in the form of a pantile construction with vapor cushions and trim device for maintaining the horizontal float position. This means that the water amounts can move on the roof to a minor degree, which requires frequent trimming with supply of air underneath the membrane and later vapor discharge directly to the atmosphere. The entry of air or vapors with the filling of the container also requires the subsequent discharge of vapors into the atmosphere.

All of the trimming operations cause major emissions. In addition, there are the unsolved emission problems during filling and emptying of the container. A floating cover of this type has thus not found any practical application.

It is the object of the present invention to minimize or rule out possible emissions and operating risks on the storage container for highly volatile hydrocarbons in all operative states and in the case of complete emptying and first filling. It should be possible to compensate for the disruption of the safe floating position by precipitations, one-sided loading, input of gaseous media into the storage liquid and leakage, and the necessity to access the floating cover should be dropped; it should be possible to carry out all operating and controlling functions from outside of the container.

This object is achieved by a vertical round container with the features of claim 1.

An essential feature of the invention is that the supply/discharge lines for the gaseous medium are connected to a central unit provided outside the container. It is possible through this central unit outside the container to vary the gaseous media in the at least one compartment such that the conditions prevailing in the compartment can thereby be adapted to the requirements. The gaseous media in the compartment can be sucked off towards the central unit or, however, supplied from the central unit to the compartment to adjust the pressure in the compartment and the level of the floating cover.

It is possible to provide a line with respect to the corresponding compartments of the floating cover that are open to the storage liquid, the line being connected to the central unit and used either as a supply line for supplying gaseous medium into the compartment or as a discharge line to discharge gaseous medium out of the compartment to the central unit; this can keep the number of the necessary lines small that pass from the central unit to the floating cover.

Particularly preferred is the arrangement of the supply/discharge lines through the liquid to the lower container edge or container bottom to connect them from there to the central unit. Possible gas escapes out of said lines can thus be entrapped again underneath the floating cover and do not pass into the atmosphere. The lines guided through the liquid should be composed of rigid line sections that are again connected by articulated adapters. With this articulated arrangement the supply/discharge lines can be adapted to the respective height level of the floating cover. To make the articulated adapters flexible so that they can be adapted to all movements of the floating cover, the articulated adapters are e.g. made of at least three hose joints.

To be able to adapt a floating cover in its horizontal orientation especially when the floating cover is moved out of its horizontal position by external loads, e.g. rainwater and snow, at least three compartments that are open towards the storage liquid should be provided around the edge portion of the floating cover. These individual compartments will then serve as trim compartments and are each connected via a separate supply/discharge line to the central unit. Thus the floating cover can be trimmed at the three points, distributed around the circumference, so that the supply or discharge of gaseous medium in the respective compartments can level the floating position of the floating cover.

Pontoon compartments closed at the liquid side may also be arranged in the peripheral portion of the floating cover, in ring-like configuration and/or in the form of sectors alternating with the trim compartments, so as to stabilize the floating position.

Furthermore, it is expedient to arrange a ring compartment that is open towards the liquid in an area positioned further towards the center, in which excessive gases and vapors or gases and vapors or gases introduced by operation error into the containers can collect centrically.

This ring compartment is not subdivided into partitioned compartments so that the same gas pressure is prevailing throughout the ring chamber.

To collect rainwater and water emanating from melting snow or ice on the upper side of the cover, a tub recessed towards the liquid is formed in the center of the cover, the bottom of the tub immersing into the liquid. The collected water is e.g. discharged through an articulated tube system out of the tub, the articulated tube system being connected on the one hand to an inlet pot in the center of the tub and on the other hand to the container wall near the bottom.

In comparison with the former constructions of floating covers with small ring pontoon and large middle membrane the area of the tub is considerably reduced. The water is therefore more concentrated in the center of the floating cover and a possible list of the floating cover due to displacement of the collected water and wind load, one-sided frictional forces or other one-sided loads, is avoided.

The water amount collected in the tub can be adjusted or discharged by controlling the level in response to the requirements. Expediently, a certain minimum water amount is left in the tub during summer operation to exploit evaporation cooling for the storage liquid.

The central unit, as has been mentioned above, should comprise at least one gas control unit with a collection line, a compressor and a distributor line and valves so that each supply/discharge line is connectable to each other supply/discharge line via the compressor. Such an arrangement has the advantage that gaseous medium, which is e.g. discharged out of a chamber to the central unit, can be supplied through corresponding switching of the valves and via the compressor into another compartment so as to adjust the horizontal floating position of the floating cover.

Discharge of ecologically harmful gases or vapors into the atmosphere is thereby avoided.

The liquid/vapor balance in the compartments open towards the liquid remains undisturbed and the further evaporation of the stored liquid is suppressed.

The potential emissions on peripheral portions of the floating cover or other emission portions (guide, control and measurement devices) can be supplied by applying a minor vacuum by means of suction lines and a compressor to the central unit of a gas utilization device following the central unit.

Likewise, the gases or vapors arising underneath the floating cover upon first filling or residual emptying of the container can be sucked in via a compressor and supplied to a gas utilization device.

In case of leakage of the floating cover it is possible to press air into the compartments open towards the liquid via the central unit and the supply/discharge lines and to carry out a provisional repair of the leakage places, if necessary.

The articulated tube system already mentioned above, which is used for discharging precipitations out of the tub, is normally of a constructionally stable design, so that such a water outlet line can be simultaneously used as a support element for the supply/discharge lines to the individual compartments and further emission sources in that said supply/discharge lines are guided along said water outlet line.

Likewise, it is possible to supply a protective gas or inert gas to the various zones of the floating cover via the supply/discharge lines and suction lines instead of air. This can be expedient for avoiding harmful reactions or for avoiding enhanced corrosion in the open compartments of the floating cover.

To be able to detect the floating position of the floating cover, devices may be provided for determining the immersion depth of the cover, preferably at extreme points, and to adjust the horizontal position of the cover through displacement of the gaseous media into the respectively downwardly open compartments in dependence upon said measurement values.

The trim compartments, as indicated above, can be arranged underneath pontoon compartments, especially when already existing floating covers are to be retrofitted with such trim compartments.

Likewise, in case of retrofitting underneath the pontoon compartments and alternating with the trim compartments, downwardly open vapor collection compartments may be arranged that form a vapor ring compartment by being interconnected at the gas side.

Further advantageous designs become apparent from the sub-claims and from the following description of embodiments with reference to the drawing, in which

FIG. 1 is a vertical longitudinal section through the center of a vertical round container with floating cover without fixed roof with central unit located outside the container and with lines guided through the liquid chamber of the container and a detail drawing A of the sealing system between container wall and floating cover.

FIG. 2 is a section corresponding to FIG. 1, but with a round container with fixed roof, and a detail B which shows a suitable sealing system for floating covers of a small overall height.

FIG. 3 is a horizontal section through the round container of FIG. 1 along the sectional line III-III in FIG. 1, but only for the steel construction of the container with floating cover.

FIG. 4A is a schematic vertical sectional view of a further floating cover.

FIG. 4B is a schematic illustration which shows the division of the floating cover into compartments, along the sectional line IV-IV in FIG. 4A.

FIG. 5 is a section, comparable with the sectional illustration of FIG. 4A, through a further design of a floating cover.

FIG. 6 is a further sectional illustration, comparable with that of FIG. 5, for a further design of a floating cover.

FIG. 7 is a schematic illustration of the structure of the central unit, as can be seen in FIGS. 1 and 2.

FIG. 8 shows a floating cover retrofitted with trim compartments and a vapor ring compartment.

FIG. 1 shows a vertical round container 1 comprising a container bottom 2 and a container wall 3; said round container 1 is filled with storage liquid 4 up to a liquid surface, designated by reference numerals 5 a, 5 b, 5 c. This round container 1 is of the type without fixed roof.

The liquid surface 5 b, 5 c of the storage liquid 4 is covered with a floating cover 6, also called floating roof. Said floating cover 6 is provided in the exterior region with a circular ring-shaped cover plate 7 a, 7 b, 7 c which is slightly inclined towards the center of the container, and includes, in the center of the floating cover 6, a tub 8 which is deepened towards the storage liquid 4, formed of the bottom 9 and the side wall 10, the bottom 9 of the tub immersing into the storage liquid 4. A pot-shaped recess 11 is formed in the center of the tub. Said tub 8 serves to collect rainwater and melt water in the central region of the floating cover 6.

In the external region of the floating cover 6, two rows of compartments are provided, arranged in ring-like fashion around the center. In the section of the floating cover 6, as can be seen in FIG. 1, the two compartments located to the right side are compartments that are open to the underside, i.e. towards the liquid 4, and are separated by a vertical partition wall 13. Said downwardly open compartments are designed in the outer region as individual and locally partitioned trim compartments 14 and further to the inside as one-part and concentric vapor ring compartments 12. At the left side of the cover 6, a pontoon compartment 15 provided with bottom plate 15 a is arranged in the external region. At the radially interior side of the pontoon compartment 15 the vapor ring compartment 12 is positioned corresponding to the opposite side.

The area of the container wall 3 and the floating cover 6 with the pontoon compartment 15 and a part of the vapor ring compartment 12 is shown as detail “A” on an enlarged scale.

As can be seen with reference to said detail drawing “A”, the ring compartment 16 between the container wall 3 and the peripheral plate 17 of the floating cover 6 is sealed with a bipartite peripheral seal 20; said peripheral seal 20 comprises a primary seal 18 and a secondary seal 19. The primary seal 18 is held by means of support arms 21 a on the peripheral plate of the floating cover 6 and is pressed against the inside of the container wall 3.

The slide plate 22 resting on the container wall 3 immerses into the storage liquid (surface 5 a) and forms a closed vapor chamber together with the seal membrane 23 a and the peripheral plate 17. The secondary seal 19 consists of support arms 21 b and the seal profile 23 c and the sealing membrane 23 b. A space 24 is formed between primary seal 18 and secondary seal 19.

Furthermore, detail drawing A shows a pontoon manhole with lid 25 to permit access into the pontoon compartment 15 for control purposes.

A foam wall plate 26 rises vertically upwards from the cover plate 7 a, 7 b of the cover 6 near the peripheral seal 20. Furthermore, FIG. 1 shows a plurality of floating roof supports 27, evenly distributed over the cover 6, which are held in guide members and are adjustable to a desired height; said floating roof supports 27, which project beyond the underside of the cover 6, serve to carry the cover 6 on the container bottom 2 whenever the vertical round container 1 is in an emptied state, so that the underside of the cover 6 is accessible, for example for maintenance purposes.

The container 1 is equipped with a line system which is connected to a central unit 28. Said line system comprises a respective supply/discharge line 29 which connects each trim compartment 14 and the vapor ring compartment 12 to the central unit 28. The connection which is passed through the storage liquid 4 underneath the cover 6 is established by three rigid line sections 30 which are connected via articulated adapters 31. Owing to these articulated adapters 31 the supply/discharge line 29 can adapt to the different height positions of the cover 6 with a varying liquid surface 5.

Furthermore, a water outlet line 32 extending from the pot-shaped recess 11 is provided, which line in turn is composed of three rigid line sections 33 and three articulated sections 34, corresponding to the supply/discharge line 29. Water collected in the tub 8 is drained via this water outlet line 32 into a drainage channel 35 outside of the container 1 via a shut-off valve 36. At the other side of the water outlet line 32, both a pneumatic valve 37 and a hand valve 38 are positioned in the area of the pot-shaped recess 11 to drain water out of the tub 8 by remote control, e.g. from a central measuring station, or in the event of failure by hand, then via the hand valve 38. Since the water outlet line 32 is given a relatively large size, thereby showing a specific stability, said water outlet line 32 can serve to hold and support the much thinner supply/discharge lines 29 and the corresponding line sections 30, respectively.

Suction lines 39 for sucking off vapors are provided in special emission zones of the cover 6; as can particularly be seen in detail drawing A, this is a suction line 39 which sucks off the vapors from the ring compartment 16 underneath the primary seal 18, and a further suction line 39 which sucks off gases from the space 24 between the primary seal 18 and the secondary seal 19. Further suction lines can be connected to fittings and to measuring and guiding elements of the floating cover 6, which are here not shown. These lines 39 are also passed to the central control unit 28. Finally, various level measuring devices are provided in the following way:

Level measuring devices 40 a are positioned on the edge of the cover 6 in the area of the ring chamber 16 to determine the floating position of the cover 6 relative to the liquid level 5 a. Further level measuring devices are provided in every trim compartment 14 and in the vapor ring compartment 12 to determine the liquid level 5 b, 5 c in the individual compartments.

Finally, a level measuring device 41 is also positioned in the area of the tub 8.

Overpressure/vacuum safety devices 45, which are connected to the cover plates 7 b, 7 c, are assigned as additional safety devices to each trim compartment and the vapor ring compartment.

It should be noted that all lines, no matter whether these are supply/discharge lines 29 for gaseous media, suction lines 39 or measurement and control lines 42, 43, e.g. for level regulation, are passed through the storage liquid 4 along the rigid line sections 32.

FIG. 3 shows a section taken through the round container 1 of FIG. 1 along the sectional line III-III to show the subdivisions of the compartments arranged in the two outer rings. The outer ring has arranged therein in alternating fashion a trim compartment 14, i.e. a compartment that is open towards the storage liquid 4 on the underside, and a pontoon compartment 15, i.e. a compartment closed at the liquid side.

The large-volume trim compartments 14 and pontoon compartments 15 are however protected by vertical compartment reinforcements 44 against dents. Connection openings 44 a are positioned in the upper area of the compartment reinforcements 44. Likewise, connection openings 44 a are provided in all compartment reinforcements 44 of the vapor ring compartment 12, so that the vapor ring compartment 12 for gases forms a single chamber.

On the right container wall 3, near the container bottom 2, the container wall has provided thereon an inlet pipe 46 which while being directed towards the container center carries an inlet diffuser 47 through which the storage liquid flows into the container. The inlet diffuser 47 has the function to prevent swirls in the liquid chamber caused by high inlet velocities. With specific filling operations, e.g. unloading of a ship or filling via pipeline, air or gas may enter together with the liquid. The gases rising in the liquid accumulate underneath the floating cover 6.

The purpose of the different functional zones of the floating cover 6 can be explained with reference to FIGS. 1 and 3.

If air or gas enters while the container 1 is being filled, the gaseous medium can rise into the vapor ring compartment 12.

Since the vapor ring compartment 12 is a one-part chamber, the entry of gaseous medium does not lead to an uneven distribution of the buoyant force over the area, but to a uniform increase in buoyancy for the floating cover. Gaseous medium entering, however, into the trim compartments 14 can be displaced via the supply/discharge lines 29, in combination with the central unit 28, into the vapor ring compartment 12.

Upon occurrence of an eccentric load on the floating cover 6, e.g. caused by a one-sided snow load, the floating cover will develop a list which might be enhanced by moving water quantities in the tub 8 and uneven frictional forces on the edge of the floating cover and endanger the safe floating position.

Gaseous medium can now be removed by means of the supply/discharge lines 29 and the central unit 28 from a trim compartment 14, which is diametrically opposite the list of the floating cover 6, and can be pressed into a trim compartment 14 in the area of the list. The floating cover is thereby moved again into its horizontal float position.

The pontoon compartments 15, the vapor ring compartment 12 and the tub 8 provide the basic load of buoyancy, with the buoyant forces of the vapor ring compartment 12 and the tub 8 being variable. What can not be changed are only the buoyant forces of the pontoon compartments 15.

To carry out the transfer operations underneath the compartments that are open towards the liquid, the central unit 28 is equipped with a line and valve system, as is schematically shown in FIG. 7.

The central unit 28 comprises a number of supply/discharge lines 29 leading to the floating cover 6. All of the supply/discharge lines 29 are connected via a respective shut-off valve 50 to a collection line 51 and a compressor 52.

Feed lines 53 for air, protective gas and other gaseous media, which are shut off by valves 55, are also connected to the collection line 51.

At the output side of the compressor 52 a distributor line 53 is provided with branch lines 56 leading to each supply/discharge line 29, said lines being adapted to be shut off by valves 57, as well as an output line 58 which leads e.g. to a vapor recovery system 60 or a refinery gas line, connectable via a valve 59.

Each supply/discharge line 29 can be connected to each other supply/discharge line 29 via the compressor 52 with the line and valve arrangement of the illustrated central gas control unit 28. All valves, which are shown in FIG. 7, are controllable individually. Furthermore, direct gas and pressure compensation between the buoyancy compartments is possible via the valves 57.

Hence, vapors entrapped underneath the floating cover 6 can be replaced underneath the trim compartments 14 for maintaining the horizontal floating position. In case of leakage external air can be introduced into the appropriate compartments 12, 14 for maintaining the necessary buoyancy. To reduce the risk of fire and to mitigate corrosive action, inert gases or dried air, respectively, can be introduced into the compartments that are open towards the liquid.

Furthermore, a pressure measuring device, which is represented in FIG. 7 for instance by unit 200, is provided for each compartment 12, 14.

The switching scheme of the central unit 28 of FIG. 7 can be switched over for a period so long that the above-mentioned connection option for the individual compartments is enabled via the compressor.

While a container 1 that is open at its upper side has been described with reference to FIG. 1, FIG. 2 shows a round container 1 that is closed on its upper side with a fixed roof 61, aerated via vent holes 61 a, 61 b.

It should be noted that in the individual figures and insofar as identical or similar structural members are shown, these are designated throughout the individual figures with the same reference numerals, so that the illustration for one figure can be applied by analogy to the respectively other figure, without the structural member being once again described in detail in the other figure.

Since the interior of the container 1 of FIG. 2 is covered by the fixed roof 61, no water-collecting tub is formed in the central region of the floating cover 6.

The floating cover 6 comprises an individual vapor collection compartment 62 which is open towards the storage liquid and formed by a covering membrane 63 and a ring-like box 64 immersing at the container wall side into the liquid 4, which, in turn, consists of an outer peripheral plate 17, an inner foam wall plate 26 and a bottom plate 65.

A vapor cushion is always located between membrane 63 and liquid surface 66. To increase the float stability, individual pontoon compartments may be directly welded to the membrane 63.

A supply/discharge line 29, with connection to the central gas control unit 28, is connected to the vapor collection compartment 62 in the center of the membrane 63.

When the container is being filled and emptied, vapors can be discharged via the gas control unit 28 out of the container, as in the case of excessive vapor underneath the membrane 63 at high operating temperatures.

The detail drawing B in FIG. 2 shows a peripheral seal 20 which is modified in comparison with the detail drawing A in FIG. 1, the peripheral seal 20 comprising a combined primary/secondary seal with a primary sealing blanket 67 and a secondary sealing blanket 68 and two sealing elements 69 and 70 on the container wall side, with interposed gas chamber 71.

Suction lines 39 are passed to the vapor chamber between liquid level 5 a and primary sealing blanket 67 and to the gas chamber 71.

At high storage temperatures the membrane 63 will bulge upwards, thereby increasing the vapor chamber. The whole floating cover 6 is floating on a vapor cushion increasing in size.

Excessive vapor can be pressed out of the ring chamber 16 underneath the primary sealing blanket 67 by means of the suction line 39 and the gas control unit 28 into the vapor collection chamber 62.

Possible vapor emissions can be sucked out of the gas chamber 71 between the sealing elements 69 and 70 by means of the suction line 39 by the central gas control unit and supplied to a vapor recovery means 60.

The arrangement is additionally provided with a supply line 72 via which fire foam can be supplied on openings 72 a; this line 72 can also be designed in case of overfilling as a withdrawal line out of this area; such overfilling may e.g. occur when the storage container has been overfilled by mistake.

It should be noted that all lines, as are also described in FIG. 2, are passed via the central tube system 73 through the storage liquid 4.

FIGS. 4A and 4B schematically show a further construction of the floating cover, which is suited for containers with a large diameter.

In contrast to the embodiment shown in FIG. 1, a further ring with individual pontoon compartments 15 is connected on the outer edge of the tub 8, and the area of the vapor ring compartment 12 is increased.

Finally, a further ring is positioned radially further to the outside, where in conformity with FIG. 3 pontoon compartments 15 and trim compartments 14 are distributed in alternating fashion. According to the embodiment as shown in FIGS. 1 and 3, the trim compartments 14 and the vapor ring compartment 12 can be filled or emptied via the central unit 28 with different gas/vapor amounts to adjust the horizontal float position and to discharge excessive gas, if necessary.

In FIG. 4 a, reference numeral 75 designates snow loads and reference numeral 76 designates gases or vapors introduced into the container. The disruption of the horizontal float position caused thereby can be compensated by shifting vapor quantities into the trim compartments 14.

The illustrated construction is suited as an inexpensive alternative to the floating covers of a twin-type membrane construction, which is normally used for containers having a diameter of more than 60 m.

FIG. 5 shows a further embodiment of the floating cover 6, which can be regarded as an inexpensive design for smaller container diameters.

There are no closed pontoon compartments, but only an external ring with trim compartments 14 and a radially inwardly following vapor ring compartment 12, as well as a tub 8.

FIG. 6 shows a further embodiment of the floating cover 6, which is also expedient for large container diameters. The outer ring includes a trim compartment 14.

This is followed radially inwards by a ring comprising individual pontoon compartments 15 as well as a vapor ring compartment 12 and a tub 8.

On containers having a floating cover, leakage damage due to individual pontoon compartments 15 breaking up are often observed after foundation settlements and after the container jacket 3 has lost its roundness, as a result of which the floating cover may descend.

In the embodiment shown in FIG. 6, the pontoon ring 15, which is important for the floating stability, cannot be impaired by deformations of the container jacket 3 because it is not arranged on the outer rim of the floating cover 6. Possible deformations on the trim compartments 14, however, do not hint at any major problems for the float position.

With all designs of the floating cover 6 for containers without roof, corresponding to FIGS. 1, 4, 5, 6, large surface areas are occupied by trim compartments 14, pontoon compartments 15 and the vapor ring compartment 12, so that the tub 8 is given a relatively small basic area and shows a greater height for compensating purposes. The water quantities collected on the floating cover therefore stay closer to the center of the floating cover and can hardly impair the horizontal float position.

If several storage containers 1 are present for the same storage product, it is advisable to provide a joint central unit 28 for all storage containers of this group of products. This makes it possible to reduce the excessive vapor amounts to be cleaned, by way of a corresponding compensation of the vapor amounts to be shifted underneath the individual storage containers.

FIG. 8 shows an expedient retrofitting of an existing floating cover 6 with a trim compartment 14. A peripheral ring made up of individual pontoons 15 and the tub bottom 9 have arranged thereunder on the outside a peripheral plate 117 and on the inside a peripheral plate 110, and in peripheral direction the necessary compartment reinforcements and partition walls, which are here not shown.

The space under the tub bottom 9 and the trim compartments are equipped with supply/discharge lines 29 that permit a displacement of vapors and a discharge/supply line of gases, respectively, via a central unit 28, as has been explained above. Likewise, it is possible to arrange downwardly open vapor collection compartments alternating with trim compartments 14 on the circumference of the floating cover 6, said vapor collection compartments forming a vapor ring compartment 12 through interconnections at the gas side, the vapor ring compartment 12 generating uniform buoyancy over the whole surface. 

1.-19. (canceled)
 20. A vertical round container for storing liquids, comprising a floating cover covering the surface of the liquid, the cover being sealed in relation to the container wall by means of flexible sealing elements and comprising, on the lower side thereof, compartments which are open towards the liquid and in which gaseous media/vapors are entrapped, devices being provided for determining the immersion depth of the cover, and supply lines and discharge lines being provided for varying the amount of the gaseous medium in the compartments, the supply lines being connected to a unit for gaseous medium that is arranged outside the container chamber, the improvement wherein both the supply lines and the discharge lines are connected to the central unit, and a gas control unit is provided and the compartments which are open towards the liquid are connected to said gas control unit which comprises a collection line, a compressor, a distributor line and valves in such a manner that each supply/discharge line of the open compartments is interconnectable to each other supply/discharge line of the other compartments via the compressor, and wherein the horizontal position of the cover is adjustable through displacement of the gaseous media/vapors between the compartments by means of the gas control unit.
 21. The container according to claim 20, wherein the gas control unit is part of the central unit.
 22. The container according to claim 20, wherein each open compartment comprises a line which is usable either as a supply line or as a discharge line.
 23. The container according to claim 20, wherein the immersion depth of the cover is determined at extreme points on the edge of the cover and in the open compartments and at least three open compartments are distributed at least around the peripheral portion of the cover, which compartments serve as trim compartments which are each connected via a separate supply/discharge line to the gas control unit.
 24. The container according to claim 20, wherein the supply/discharge lines are passed through the liquid to the lower container edge or container bottom.
 25. The container according to claim 24, wherein the lines guided through the liquid are composed of rigid line sections which are connected by articulated adapters.
 26. The container according to claim 25, wherein at least three hose joints are provided as articulated adapters.
 27. The container according to claim 26, wherein, when viewed in circumferential direction and/or towards the container center, pontoon compartments, each closed at the liquid side, are provided to alternate with the trim compartments.
 28. The container according to claim 20, wherein the cover has provided thereon at least one concentric vapor ring chamber which is connected via a separate supply/discharge line to the central unit.
 29. The container according to claim 28, wherein the vapor ring compartment is arranged in a portion positioned further to the center of the cover.
 30. The container according to claim 20, wherein a tub deepened towards the liquid is formed in the center of the cover, the bottom of the tub immersing into the liquid.
 31. The container according to claim 20, wherein the central unit comprises supply lines for air and other gases and a vapor discharge line.
 32. The container according to claim 20, wherein suction lines which are connected to the central unit are provided in the area of the flexible sealing elements and further emission zones of the cover.
 33. The container according to claim 20, wherein in the center of the cover a water outlet line or a feed line for fire foam or another feed/disposal line is connected to the cover which assumes a supporting and carrying function for the supply/discharge lines and for suctions lines and the measurement and control lines.
 34. The container according to claim 30, wherein the tub is provided with a water-level measuring device (41) and level-regulating device.
 35. The container according to claim 23, wherein the trim compartments are disposed underneath pontoon compartments.
 36. The container according to claim 28, wherein a vapor ring compartment which is formed by vapor collection compartments connected at the gas side is arranged underneath the pontoon compartments.
 37. An arrangement comprising a plurality of containers according to claim 20, wherein said containers are connected to a joint central unit. 